Periodic bandwidth widening for inductive coupled communications

ABSTRACT

A method of inductive coupled communications includes providing a first resonant tank (first tank) and a second resonant tank (second tank) tuned to essentially the same resonant frequency, each having antenna coils and switches positioned for changing a Q and a bandwidth of their tank. The antenna coils are separated by a distance that provides near-field communications. The first tank is driven to for generating induced oscillations to transmit a predetermined number of carrier frequency cycles providing data. After the predetermined number of cycles, a switch is activated for widening the bandwidth of the first tank. Responsive to the oscillations in the first tank, the second tank begins induced oscillations. Upon detecting a bit associated with the induced oscillations, a switch is activated for widening the bandwidth of the second tank and a receiver circuit receiving an output of the second tank is reset.

CROSS-REFERENCE TO COPENDING APPLICATIONS

This application has subject matter related to copending applicationSer. No. 14/289,895 entitled “METHOD AND APPARATUS FOR DIE-TO-DIECOMMUNICATION” that was filed on May 29, 2014.

FIELD

Disclosed embodiments relate to resonant inductive coupled communicationsystems.

BACKGROUND

Resonant inductive coupling (or electromagnetic induction) is thenear-field wireless transmission of energy between two inductors (coils)between resonant circuits tuned to resonate at about the same frequency.The respective coils may exist as a single piece of equipment orcomprise two separate pieces of equipment.

The general principle of energy transfer and efficiency for resonantinductive coupling is that if a given oscillating amount of energy (forexample a pulse or a series of pulses) is forced into a primary(transmitting) coil which is capacitively loaded, the coil will “ring”,so that oscillating fields will occur, with the field energytransferring back and forth between the magnetic field in the inductorand the electric field across the capacitor at the resonant frequency.This oscillation will decrease (damp) over time at a rate determined bythe gain-bandwidth (Q factor) of the resonant circuit, mainly due toresistive and radiative losses. However, provided the secondary(receiving) coil cuts enough of the magnetic field that it absorbs moreenergy than is lost in each cycle of the primary (transmitting) coil,then most of the transmitted energy can still be transferred.

The primary coil is generally the L part of a series RLC resonantcircuit (resonant “tank”), and the Q factor for such a resonant tank isgiven by:

$Q = {\frac{1}{R}\sqrt{\frac{L}{C}}}$

For example for R=20 ohm, C=1 μF and L=10 mH, Q=5. Because the Q factorfor the resonant tank can be very high, only a small percentage of themagnetic field needs to be coupled from one coil to the other coil toachieve a reasonably high energy transfer efficiency, even though themagnetic field decays quickly with increasing distance from a coil, theprimary coil and secondary coil can be several diameters apart. It canbe shown that a figure of merit for the energy transfer efficiency (U)from primary coil and secondary coil is the following:

U=k√{square root over (Q ₁ Q ₂)}

Where k is the coupling coefficient, and Q1 and Q2 are the Q's for theprimary (transmitting) tank and secondary (receiving) tank. Althoughassuming a reasonable k-value (k<1) the energy transfer efficiency forthe resonant inductive coupled communication system can be high, thedata rate may be limited because for a communication channel the maximumdata-rate that can be achieved is limited by the channel's bandwidth,which is given by the Q of the tank (higher Q means a lower bandwidth).For example, for a tank tuned at 1 GHz with a Q of 10, the bandwidth isonly 100 MHz. For example, for a binary modulation scheme (e.g., ON-OFFkeying), the maximum data-rate is 2× the available bandwidth, governedby the well-known Nyquist theorem.

SUMMARY

This Summary briefly indicates the nature and substance of thisDisclosure. It is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims.

Disclosed embodiments recognize the above-described data rate limitationfor resonant inductive coupled communication systems is particularlyproblematic when high speed data transfer is needed. For example, it maybe desirable to achieve a 400+ Mb/s data rate between semiconductor(e.g., silicon) die having respective resonant tanks with on-chipantenna coils, where in one example the tank bandwidth is <½ the desireddata rate, such as about 130 MHz in one particular embodiment. Thismakes the desired minimum communication data rate of 400 Mb/s for binarycommunications not possible as this data rate is >2× bandwidth, whichviolates the Nyquist theorem.

Disclosed embodiments include methods of inductive coupledcommunications includes providing a first resonant tank (first tank) anda second resonant tank (second tank) tuned to essentially the sameresonant frequency, each having antenna coils and switches positionedfor changing a Q and a bandwidth of their tank. By adaptively changingthe Q of the transmitter and receiver tanks the above-described datarate problem is solved. The antenna coils are separated by a distancethat provides near-field communications. The first tank is driven tooscillate to transmit a predetermined number of carrier frequency cyclesproviding data. After the predetermined number of cycles, a switch isactivated for widening the bandwidth of the first tank. Responsive tothe oscillations in the first tank, the second tank begins inducedoscillations. Upon detecting a bit associated with the inducedoscillations, a switch is activated for widening the bandwidth of thesecond tank and a receiver circuit receiving an output of the secondtank is reset.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, wherein:

FIG. 1 is a flow chart that shows steps in an example method of resonantinductive coupled communications including periodic bandwidth widening,according to an example embodiment.

FIG. 2A is a depiction of a lateral multichip mode (MCM) packageimplementing disclosed resonant inductive coupled communicationsincluding periodic bandwidth widening having respective die shown as Die1 and Die 2 on a split lead frame of the MCM to achieve a high isolationvoltage between the Dies, according to an example embodiment.

FIG. 2B is a depiction of a vertical MCM package implementing disclosedresonant inductive coupled communications including periodic bandwidthwidening having respective die shown as Die 2 on Die 1 stacked on a diepad of the lead frame, according to an example embodiment.

FIG. 3A depicts an example arrangement for implementing a forcedresonance of a tank, according to an example embodiment, and FIG. 3Bdepicts the input modulated carrier drive signal waveform and theresulting waveform across the antenna coils, according to an exampleembodiment.

FIG. 4 top plot depicts the effect of disclosed de-Qing on a tankaccording to an example embodiment vs. an otherwise equivalent tankwithout disclosed de-Qing, and the bottom plot depicts last stage bufferoutput as a function of time for the disclosed transmitter tankemploying de-Qing.

FIG. 5A depicts an example resonant inductive coupled communicationssystem embodiment including two coupled series tanks according to anexample embodiment, and FIG. 5B depicts waveforms for the NMOS switchesSW2, SW1 and transmitter voltage (Vxmtr) according to an exampleembodiment.

FIG. 6A depicts receiver output waveforms across a receiver tank withoutdisclosed De-Qing and FIG. 6B depicts receiver output waveforms acrossan otherwise equivalent receiver tank including disclosed De-Qing,according to an example embodiment.

FIG. 7 shows block diagram depictions of another example receiver sensecircuit architecture, according to an example embodiment.

FIG. 8 shows results from a transient simulation across the receivertank for a 400 Mbps data input (01010100110011000111) showing the datainput at the top and the data output for the receiver tank on thebottom, according to an example embodiment.

DETAILED DESCRIPTION

Example embodiments are described with reference to the drawings,wherein like reference numerals are used to designate similar orequivalent elements. Illustrated ordering of acts or events should notbe considered as limiting, as some acts or events may occur in differentorder and/or concurrently with other acts or events. Furthermore, someillustrated acts or events may not be required to implement amethodology in accordance with this disclosure.

Also, the terms “coupled to” or “couples with” (and the like) as usedherein without further qualification are intended to describe either anindirect or direct electrical connection. Thus, if a first device“couples” to a second device, that connection can be through a directelectrical connection where there are only parasitics in the pathway, orthrough an indirect electrical connection via intervening itemsincluding other devices and connections. For indirect coupling, theintervening item generally does not modify the information of a signalbut may adjust its current level, voltage level, and/or power level.

Disclosed embodiments provide communication methods for resonantinductive coupled communication systems, where the respective tanks eachinclude switches that periodically reset the system memory andperiodically widen the channel bandwidth (e.g., by adding resistance) toachieve a high data rate, beyond (above) the Nyquist data rate.Disclosed embodiments include methods of resonant inductive coupledcommunications including providing a first resonant tank (first tank)tuned to a first resonant frequency including a first switch, a firstcapacitor and a first antenna coil where the first switch is positionedfor changing a Q and a bandwidth of the first tank, and a secondresonant tank (second tank) tuned to a second resonant frequency that isessentially equal the first resonant frequency including a secondswitch, a second capacitor and a second antenna coil wherein the secondswitch is positioned for changing a Q and a bandwidth of the secondtank. As used herein, tank resonant frequencies being “essentiallyequal” is defined to be within 10% of one another. The first antennacoil and second antenna coil are separated from one another by adistance that provides near-field communications defined herein asdistance providing a minimum coupling coefficient (k) of 0.01 (or moreprecisely k*(Q1*Q2)^(1/2)>0.1) The respective resonant tanks can beseries resonant tanks or parallel resonant tanks.

The first tank is driven to oscillate with a modulated carrier signal sothat the first antenna coil transmits a predetermined number of carrierfrequency cycles (predetermined number of cycles) providing data that isfirst transition coded (i.e., a 0 to 1 transition or a 1 to 0 transitiontriggers transmission of carrier pulses). After the predetermined numberof cycles, the first switch is activated for widening the bandwidth ofthe first tank referred to herein as de-Q'ing responsive to theoscillations in the first tank. Through inductive coupling the secondtank begins induced oscillations, wherein upon a receiver circuitcoupled to receive an output of the second tank detecting a bitassociated with the induced oscillations, the second switch is activatedto widen the bandwidth of the second tank (de-Qing) and the receivercircuit is reset.

By disclosed embodiments adaptively de-Q'ing the receiver tank, thereceived signal strength can be decoupled (independent) from the speedof the receiver tank. Disclosed switching allows the maximum available Qof the receiver tank to be used to provide a high received signalstrength, and adaptive de-Q'ing allows the receiver tank during othertime intervals to achieve higher speed by adaptively increasing itsbandwidth.

FIG. 1 is a flow chart that shows steps in an example method 100 ofresonant inductive coupled communications, according to an exampleembodiment. Step 101 comprises providing a first resonant tank (firsttank) tuned to first resonant frequency including a first switch, afirst capacitor and a first antenna coil, wherein the first switch ispositioned for changing a Q and a bandwidth of the first tank, and asecond resonant tank (second tank) including a second switch, a secondcapacitor and a second antenna coil, wherein the second switch ispositioned for changing a Q and a bandwidth of the second tank. Thesecond tank is tuned to a second resonant frequency that is essentiallyequal to the first resonant frequency. The first antenna coil and secondantenna coil are separated from one another by a distance that providesnear-field communications, such as from 0.5 mm to 2 mm.

Step 102 comprises driving the first tank for generating inducedoscillations with a modulated carrier signal so that the first antennacoil transmits a predetermined number of carrier frequency cycles(predetermined number of cycles) providing data that is first transitioncoded (see e.g., FIG. 8 described below). Hence for a “0” to “1”transition or a “1” to “0” transition, a fixed set of carrier frequencycycles are transmitted. In step 103, after the predetermined number ofcycles, the first switch is activated for widening the bandwidth andlowering the Q (De-Qing) of the first tank. For example, after thepredefined number of cycles, a series resistor can be switched into thetransmitter tank to widen its bandwidth and De-Q the tank for hasteningthe clearing of the tank memory manifested by its ringing (e.g., seeresistor R 318 and NMOS 305 SW1 in FIG. 5A described below).

Step 104 comprises responsive to the oscillations in the first tank,through inductive coupling, the second tank begins induced oscillations.The induced oscillations are amplified and detected by receiver sensecircuitry coupled to an output of the second tank (e.g., see receiversense circuit 570 shown in FIG. 5A described below).

In step 105 upon detecting a bit associated with the inducedoscillations, the second switch is activated to widen the bandwidth andreduce the Q of the second tank (De-Qing the second tank), and areceiver circuit coupled to receive an output of the second tank isreset. For example, when a bit is detected, the receiver can promptlybegin to clear the receiver's channel memory (its ringing) to hastengetting ready for the next bit, as it is recognized herein a new bitcannot be received while the second tank is still ringing. This way, thereceiver is not limited its tanks' bandwidth. Using a receiver switch, aresistor (or capacitor) can be brought in parallel to the receive tankto reset (De-Q) it (widening the tank bandwidth) (see NMOS 305 SW1 and R318 in FIG. 5A described below). The other circuit ringing sources(e.g., filters) can be reset using a ground side switch.

The detection of a bit and subsequent control of the reset switch in thereceiver tank can be accomplished using embedded hardware (embeddeddigital circuits and state machine) with a block level example of areceiver sense circuit 570 shown in FIG. 5A described below. A complexprocessor or microcontroller is not needed because the decisiongenerally needs to be rendered fast as the loop settling time (timetaken for bit detection to reset) determines the speed of operation(data rate).

Although as defined above near-field communications is defined asdistance providing a minimum U=k*(Q1*Q2)^(1/2) of 1, disclosed designsgenerally target a minimum U>0.1 for efficiency and receiver complexityand robustness of the design. Lower k values (larger coil separation)can be used with a more sophisticated receiver, which will generallyinvolve more power and chip area.

A product of the maximum Q for the first tank and a maximum Q for thesecond resonant tank can be ≧50. The tank Q achievable for ICs istypically limited to 8 to 15. The Q can be higher (e.g., up to 35) forspecial processes with very thick metal such as copper. A particularvalue of Q is generally not important for disclosed embodiments as thede-Q mechanism described herein enables working with a large variationof Q.

The modulated carrier signal is generally at a carrier frequency from500 MHz to 4 GHz. The carrier frequency is generally chosen based onconsiderations including the process capability, and data rate needed.In one particular design, a frequency of 2 GHz is chosen for a 180 nmsemiconductor (e.g., silicon CMOS) process to achieve a data rate ofabout 400 Mb/s. One will generally need to utilize higher frequency forhigher data rates. One can come down in frequency (e.g., to 500 MHz) ifthe needed data rate is lower. However, lower frequency oscillators aregenerally bulky (large L and/or large C).

FIG. 2A is a depiction of a lateral MCM package 200 implementingdisclosed resonant inductive coupled communications including periodicbandwidth widening having respective die shown as Die 1 and Die 2 on asplit lead frame 210 having a first die pad 210 a and a second die pad210 b to achieve high voltage isolation (e.g., several thousand volts)between the respective Die, according to an example embodiment. The bondwires and leads for split lead frame 210 are not shown in FIG. 2A forsimplicity. Inductive coupled communications are established between Die1 and Die 2 with magnetic coupling between on-chip antenna coils 201 and202 that are within respective resonant tanks with a first tank on Die 1and a second tank on Die 2, where the respective tanks are tuned withcapacitors to resonate at essentially the same tank frequency.

Although the antenna coils 201 and 202 are shown being on chip for Die 1and Die 2, the antenna coils can also be off chip. The Die 1 to Die 2breakdown characteristics of MCM 200 is generally determined by the moldcompound (e.g., epoxy mold material) shown as mold 218 present betweenthe respective Die. The separation distance between Die 1 and Die 2 isshown as being 0.5 mm to 1 mm as an example, but can be varied toprovide different breakdown voltages. There is generally no common modetransient immunity (CMTI) issue as loop currents do not form in theantenna coils 201 and 202 due to common mode transients. Since themagnetic field is set up only when loop current flow through the antennacoils 201 and 202, a CMTI event generally does not cause any issues.Active circuits (e.g., CMOS circuits) can be implemented on Die 1 andDie 2 along with the antenna coils, such including a local oscillatorand modulator on the transmitter die and a receiver circuit on thereceiver die. Also, other functions, such as data-converters, high speedinput/outputs (I/Os), microcontrollers, etc. can also be implemented onthe same die.

FIG. 2B is a depiction of a vertical MCM package 250 implementingdisclosed resonant inductive coupled communications including periodicbandwidth widening having respective die shown as Die 1 and Die 2stacked on a die pad 260 a of a lead frame 260, according to an exampleembodiment. The bond wires and leads for lead frame 260 are again notshown in FIG. 2B for simplicity. A dielectric layer 257 is shown betweenDie 1 and Die 2. In one arrangement Die 2 can be coupled to Die 1 usingthrough-silicon via (TSV) technology. There can be mold between the Diesin a stacked face-to-face assembly, or there can be a laminate materialbetween the respective Die.

MCM 200 and MCM 250 are not dependent on any specific processtechnology. For example, any process can generally be used that providesa suitable metal stack for forming the loops for the antenna coils 201and 202. MCM 200 and MCM 250 can generally be used for a variety ofother die-to-die coupling applications. For example, the die to diecommunication can be embedded as an I/O module in system-on-chips (SOCs)having other functions, such as data-converters, high speed I/Os,microcontrollers, etc. that as noted above can also be implemented onthe same die.

FIG. 3A depicts a transmitter arrangement 300 for implementing forcedresonance of a transmitter tank 310, according to an example embodiment,and FIG. 3B depicts the input modulated carrier drive signal waveformand the resulting waveform across the transmitter coils 320 shown havinga first coil with an inductance of L and a second coil with aninductance of L. A transmit (TX) controller 330 receives in inputdriving signal shown as DATA_IN, where the TX controller 330 generatesthe modulated carrier 312 and modulated data signal complement 313shown. The driving signal can generally be any periodic wave (e.g., sineor square wave) tuned to the first resonant frequency. A localoscillator (not shown) can generate the square waves shown in FIG. 3Btuned to the resonant (natural) frequency of the transmitter tank 310which provides the carrier. This carrier is modulated by data added tothe carrier by the TX controller 330 to produce the modulated datasignal 312 and modulated data signal complement 313 shown input viabuffers 314 a and 314 b across the transmitter tank 310.

One particular example of signal processing provided by TX controller330 and a brief mention of receive processing comprises the following:

1. The input data shown as DATA_IN is first transition or edge coded,i.e. generating a few (pre-determined) carrier pulses for 0->1 and 1->0data edges. That way, when the input is steady 0 or 1 for a relativelylong time, the whole system is kept idle, conserving power.2. At the data transition edge, an oscillator (clock) is started runningat 2 GHz to send a few pulses shown as modulated carriers 312 and 313 inFIGS. 3A and 5A.3. A counter counts the number of (pre-defined) oscillator pulses andthen stops the transmission and resets the oscillator.4. At this time the RESET or DE-Q (using NMOS 305 SW1 305 a in FIG. 3A)pulse is generated, which lasts for half or one oscillator cycle, whichturns OFF NMOS 305 SW1 to de-Q the transmitter tank 310 and rapidlydissipate the tank's energy.5. The whole operation can be controlled can by a finite state machine,which can be implemented as hardwire since it runs at 2 GHz.6. The transmitted pulses are detected by a receiver sense circuitcoupled to a receiver tank as a bit edge described below relative toFIG. 5A. The receiver sense circuit then decodes this into levels andsends out the decoded information as DATA_OUT as shown in FIG. 5A.

In one possible implementation, the transmitter tank 310 is driventhrough AC coupling capacitors each shown in FIG. 3A as C1. The totaltransmitter coil inductance of 2L shown as separate L's resonate withthe parallel combination of capacitors C1 and C2. C1 and C2 can be onthe order of 1 pF. At each clock, the transmitter coils 320 receives avoltage step shown at the bottom of FIG. 3B given by:

Vstep=Vin*C1/(C1+C2)

Where Vin is the difference between the level of the modulated datasignal 312 and modulated data signal complement 313 which is 3.5 V forthe waveforms shown in FIG. 3B. A switch shown as an NMOS 305 SW1 whichincludes an enable input (gate electrode) 305 a having a resistor R 318that is in parallel to NMOS 305 SW1. NMOS 305 SW1 has an ON resistance(R_(ON))<<R 318. When NMOS 305 SW1 is not enabled by a suitablegate-to-source voltage coupled to enable input 305 a, R 310 isintroduced as a series resistance in the transmitter tank 310 forde-Qing the transmitter tank 310. When NMOS 305 SW1 is enabled (turnedON) by a suitable gate-to-source voltage coupled to enable input 305 a,R 318 is bypassed by NMOS 305 SW1, which is the higher Q state of thetransmitter tank 310 used for normal transmit operation.

For de-Qing, the NMOS 305 SW1 is opened which brings R 318 into thetransmitter tank 310. There are 2 main reasons for including R 318 intransmitter tank 310. Firstly, R 318 reduces the Q of the transmittertank 310 significantly, widening its bandwidth and quenching thetransmitter tank 310. Secondly, R 318 limits the instantaneous voltageswing across the NMOS 305 SW1, protecting it from breakdown or reverseconduction (due to negative voltage). The second feature also limits howhigh a resistance for R 318 can generally be used.

FIG. 3B depicts the input modulated carrier drive signal waveform shownas din and the resulting waveform across the pair of antenna coils shownas “tank_swing”. The input modulated carrier drive signal waveform isshown as a square wave having a 1.8 V amplitude. The modulated datasignal 312 and modulated data signal bar 313 shown in FIG. 3A allows thetransmitter tank 310 to have a tank swing that is 2 times the positivepower supply (VDD) or more, and also swing negative, shown swinging fromabout 3 V to −3V in FIG. 3B. For example, the transmitter tank 310 canswing +/−3V when coupled to a 1.8V power supply and driven by a bufferhaving 1.8V transistors. To achieve fast turn-off (referred to herein asa de-Q or Quench) of the transmitter tank 310 shown in FIG. 3B of about1 nsec, NMOS 305 SW1 acting as a series switch can be turned OFF betweenits inductors L. This series switch arrangement protects the NMOS 305SW1 from high magnitude positive and negative swings.

The top plot in FIG. 4 depicts the effect of disclosed de-Qing on atransmitter tank according to an example embodiment for the transmittertank 310 in FIG. 3A vs. an otherwise equivalent transmitter tank withoutdisclosed de-Qing (lacking NMOS 305 SW1 and R 318). Disclosed de-Qing(shown as “with De-Q”) is seen to significantly speed the damping of theoscillations compared to the waveform without disclosed De-Qing (shownas “without De-Q”). The bottom plot in FIG. 4 depicts the last stagebuffer output as a function of time for the disclosed transmitter tankemploying de-Qing. The Last stage buffer output drives the transmittertank, and is shown that only some pulses are given to the tank with 3pulses and the NMOS 305 SW1 being ON during this case. The swing of thetransmitter tank is due to these pulses only. As soon as the pulses areOFF, R 318 is brought in series by turning NMOS 305 SW1 OFF.

FIG. 5A depicts an example resonant inductive coupled communicationssystem 500 including an inductively coupled transmitter tank 510including transmitter coils 320 controlled by TX controller 330, and areceiver tank 520 including receiver coils 530, including a receiversense circuit 570 having an amplifier 571 that has inputs receiving anoutput of the receiver tank 520 (between VP_Tank and VM_Tank), accordingto an example embodiment. Receiver sense circuit 570 is shown includingan amplifier 571, rectifier and peak detector block 572, Schmitt trigger573, delay block 574, mono-shot generator 575 and digital block 576,wherein an output of the digital block 576 provides the DATA_OUT shown.The reset signal shown coupled to the rectifier and peak detector block572 and to the gate electrode of the second NMOS 525 SW2 as a Rx de-Qsignal is generated by the mono-shot generator 575. When a bit isdetected, the Schmitt trigger 573 output triggers to ‘1’ and the same isused by the mono-shot generator 575 as reset signal after a suitabledelay is provided by the delay block 574.

The transmitter tank 510 uses a combination of series and parallelcapacitors C1, C2 and C3. The series capacitors C1 and C2 (AC couplingcapacitors) are used to drive energy into the transmitter tank 510. Theseries capacitors C1 and C2 also protect the driving transistors of thedriving buffers 314 a and 314 b from the relatively high voltagegenerated at the transmitter tank 510.

The transmitter coils 320 is shown split into two equal coil parts witha NMOS 305 switch (SW1) in between. When NMOS 305 SW1 is ON, itessentially shorts the coils together and the inductors work as a singleInductor in a single LC circuit. This way, when ON, the NMOS 305 switchtransistor (SW1) only sees a very small swing across it. The tips of thecoils go through a +/−3V swing, but only a small fraction of this swingis seen by the center switch transistor NMOS 305 SW1.

Without R1 318, when the NMOS 305 SW1 switch turns OFF (for de-Qing), alarge voltage spike would ordinarily appears across NMOS 305 SW1. Thisis avoided by keeping a parallel resistor as R1 318 to SW1. Resistor R1318 restricts the swing across NMOS 305 SW1 by bypassing the current andalso dissipating energy to lower the Q of the transmitter tank 510. Thisway de-Qing or quenching of the transmitter coils 320 can be handled bya low voltage rated transistor and there is still the ability to handlenegative coil swings.

Receiver tank 520 is shown including a second NMOS 525 SW2 having anenable input (gate electrode) 525 a shown receiving a De-Q input at thegate. Resistors shown as R2 and R3 in receiver tank 520 are switchedinto the receiver tank 520 to lower the Q of the tank when the enableinput shown as a de-Q input turns on NMOS 525 SW2. The M with a doublesided arrow shown in FIG. 5A depicts magnetic coupling between thetransmitter coils 320 and the receiver coils 530.

Regarding operation of the receiver tank 520, a parallel resistance (R2and R3, e.g., about 25 Ohms each) is shown for de-Qing. This arrangementis used for 2 main reasons. Firstly, the swing in the receiver coils 530is generally small, typically being less than +/−300 mV. Accordingly,the switch transistor NMOS 525 SW2 (which sees the entire voltage swingwhen OFF) can withstand the voltage. Secondly, a switch in series to thecoil (like the primary side) would need to have a low ON resistance andhence be large in size. As the switch transistor NMOS 525 SW2 isgenerally a large area transistor, when being turned ON and OFF it cansetup parasitic oscillations, which can be falsely detected as a signal.Hence a series switch (NMOS 305 SW1) used in the transmitter tank 510 isnot used in the receiver tank 520, and instead NMOS 525 SW2 is used as aparallel switch. In this scheme, the NMOS 525 SW2 switch is OFF fornormal operation and turns ON when the receiver tank 520 needs to bede-Qed. This operation is exactly opposite relative to the transmittertank 510.

Although not shown in FIG. 5A, there is a parasitic resistance (e.g. 5to 10 ohms) inherent to the transmitter and receiver coils that cannotbe accessed. The parasitic resistance results in a decrease in theinherent Q of the tank, which is generally desirable to maximize in fordisclosed embodiments to provide a Q of the tank of about 10 to 12. Theresistances R 528 and R 529 are shown that are switched in and out ofthe receiver tank 520 as needed as is R 318 in the transmitter tank 510.

During operation of the receiver sense circuit 570 when the receivercircuit 520 receives a 0′ bit, the 0′ bit does not have any energy init. The receiver sense circuit 570 can be reset to ‘0’ after everydetection of ‘1’ so that the Schmitt trigger 573 does not repeatedlytrigger. The receiver sense circuit 570 needs to detect the ‘1’ andreset to ‘0’ within the bit period, i.e. 2 ns for the case where one islooking to achieve a maximum data rate of 500 mbps so the decision hasto be taken in 2 ns and the system has to be reset after detection in 2ns. Ideally the receiver tank 520 will develop a peak to peak voltage of800 mV in 1.5 ns for a 1% coupling coefficient (k).

FIG. 5B depicts waveforms applied to NMOS 525 SW2, NMOS 305 SW1, andtransmitter voltage (Vxmtr) which is across the transmitter tank 510.NMOS 305 SW1 and NMOS 525 SW2 are independent to each other, andindependent decisions of switching NMOS 305 SW1 is taken in transmitterand of switching SW2 is taken in receiver. However because of switchingmechanism it appears they are out of phase, NMOS 305 SW1 in series of ithas to be ON during transmission and NMOS 525 SW2 is in parallel, so ithas to OFF during transmission else it will short the transmitter coils320. After a bit is transmitted NMOS 305 SW1 is deactivated after somedelay only bit is detected at receiver and NMOS 525 SW2 is activated, soit looks like they are out of phase. Accordingly, the phase differencebetween them depends upon delay in the system from transmitter toreceiver.

FIG. 6A depicts receiver output waveforms across a receiver tank withoutdisclosed De-Qing and FIG. 6B depicts receiver output waveforms acrossan otherwise equivalent receiver tank 520 with disclosed De-Qing,according to an example embodiment. Disclosed de-Qing is seen to againspeed the damping of the oscillations compared to the waveform withoutdisclosed De-Qing.

FIG. 7 shows a block diagram depiction of another example receiversensor architecture shown as receiver sense circuit 700, shown coupledto receive the output from a receiver tank 520 shown in FIG. 5A,according to an example embodiment. For receiver sense circuit 700 therectifier and peak detector block 572 shown within receiver sensecircuit 570 shown in FIG. 5A is replaced by a positive peak detectorblock 572 a and a negative peak detector block 572 b and the Schmitttrigger 573 shown with receiver sense circuit 570 is replaced by anamplifier 752 having an input resistor 753 and feedback resistor 754.Although not shown in FIG. 7, the Vout shown is subsequently processedby a digital block to provide a DATA_OUT signal, such by the digitalblock 576 shown as part of receiver sense circuit 570 in FIG. 5A.

Examples

Disclosed embodiments are further illustrated by the following specificExamples, which should not be construed as limiting the scope or contentof this Disclosure in any way.

Regarding example modulation schemes, since a tuned LC coupled systemprovides a bandpass channel, a carrier based modulation scheme can beused. On-off keying (OOK) is the simplest form of amplitude-shift keying(ASK) modulation that represents digital data as the presence or absenceof a carrier. A 500 Mbp/s data rate can be targeted with On/Off Keying(OOK). An example system' bandwidth is 130 MHz; which means a data rateof around 8 ns. A data rate of 8 ns means one cannot send new data forat least the next 8 ns because the tank retains memory of data sentearlier for a period 8 ns, restricting the data rate. To achieve datarate of about 500 Mbps, each bit needs to be transferred within about 2ns and system memory needs to be cleared.

A disclosed De-Q technique is employed at the transmitter and atreceiver to accomplish this desired data transfer rate. When bit ‘1’needs to be transmitted, 3 square pulses at 2 GHz are applied at thetransmitter tank. When the data is ‘0’, no signal is applied at thetransmitter tank. FIG. 8 shows results from a transient simulationacross the receiver tank for a 400 Mbps data input(01010100110011000111) showing the data input at the top and the dataoutput for the receiver tank on the bottom, according to an exampleembodiment. The data rate shown is 400 mbps operating at roomtemperature.

Those skilled in the art to which this disclosure relates willappreciate that many other embodiments and variations of embodiments arepossible within the scope of the claimed invention, and furtheradditions, deletions, substitutions and modifications may be made to thedescribed embodiments without departing from the scope of thisdisclosure.

1. A method of resonant inductive coupled communications, the methodcomprising: driving a first resonant tank (first tank) for generatinginduced oscillations with a modulated carrier signal, said first tanktuned to a first resonant frequency and including first antenna coils,so that said first antenna coils transmit a predetermined number ofcarrier frequency cycles (predetermined number of cycles) for providingdata that is first transition coded; said first tank further including:a first capacitor coupled in parallel to said first antenna coils; afirst resistor coupled in series between said first antenna coils; and afirst switch coupled in series between said first antenna coils; aftersaid predetermined number of cycles, activating said first switch forwidening a bandwidth and changing a Q factor of said first tank;responsive to said oscillations in said first tank, beginning inducedoscillations in a second resonant tank (second tank), said second tanktuned to a second resonant frequency that is essentially equal saidfirst resonant frequency and including: a second antenna coil that isseparated from said first antenna coils by a distance that providesnear-field communications; a second capacitor coupled in parallel tosaid second antenna coil; and a second switch coupled in parallel tosaid second antenna coil; and responsive to detecting a bit associatedwith said induced oscillations of said second tank, activating saidsecond switch for widening a bandwidth and changing a Q factor of saidsecond tank, and resetting a receiver sense circuit coupled to receivean output of said second tank.
 2. The method of claim 1, furthercomprising: opening said first switch to bring said first resistor intosaid first tank; and opening said second switch to remove a secondresistor from said second tank.
 3. The method of claim 1, wherein saidmodulated carrier signal is an amplitude-shift keyed (ASK) signal. 4.The method of claim 1, wherein said receiver sense circuit includes anamplifier: coupled to receive an output of said second tank at inputs ofsaid amplifier; and coupled in series to a rectifier and peak detectorand a delay block.
 5. The method of claim 1, wherein a product of amaximum Q factor for said first tank and a maximum Q factor for saidsecond tank is ≧50.
 6. The method of claim 1, wherein said modulatedcarrier signal is at a carrier frequency from 500 MHz to 4 GHz.
 7. Themethod of claim 1, wherein said first tank is formed on a first chip andsaid second tank is formed on a second chip, and said first antennacoils and said second antenna coil both comprise metal loops.
 8. Themethod of claim 7, wherein said first chip and said second chip arepositioned lateral to one another on a split leadframe within amulti-chip package (MCP), and said first chip and said second chip bothinclude mold compound thereover and therebetween.
 9. The method of claim7, wherein said first chip and said second chip are in a stackedconfiguration on a substrate within a multi-chip package (MCP).
 10. Themethod of claim 1, wherein said driving said first tank to oscillatecomprises applying a periodic wave tuned to said first resonantfrequency modulated by said data.
 11. A resonant inductive coupledcommunications system, comprising: a first resonant tank (first tank)tuned to a first resonant frequency and including: first antenna coils;a first capacitor coupled in parallel to said first antenna coils; afirst resistor coupled in series between said first antenna coils; and afirst switch coupled in series between said first antenna coils; asecond resonant tank (second tank) tuned to a second resonant frequencythat is essentially equal said first resonant frequency and including: asecond antenna coil that is separated from said first antenna coils by adistance that provides near-field communications; a second capacitorcoupled in parallel to said second antenna coil, and a second switchcoupled in parallel to said second antenna coil; receiver sensecircuitry coupled to an output of said second tank; said first tankarranged to generate induced oscillations when driven by a modulatedcarrier signal, so that said first antenna coils transmit apredetermined number of carrier frequency cycles (predetermined numberof cycles) for providing data that is first transition coded; a transmitcontroller for activating said first switch for widening a bandwidth andchanging a Q factor of said first tank after said predetermined numberof cycles; said second tank arranged to begin induced oscillationsresponsive to said oscillations in said first tank; and said receiversense circuitry arranged to activate said second switch for widening abandwidth and changing a Q factor of said second tank and to resetitself, responsive to detecting a bit associated with said inducedoscillations of said second tank.
 12. The system of claim 11, wherein:opening said first switch is for bringing said first resistor into saidfirst tank; and opening said second switch is for removing a secondresistor from said second tank.
 13. The system of claim 11, wherein saidfirst tank is formed on a first chip and said second tank is formed on asecond chip, and said first antenna coils and said second antenna coilcomprise metal loops.
 14. The system of claim 13, wherein said firstchip and said second chip are positioned lateral to one another on asplit leadframe within a multi-chip package (MCP), and said first chipand said second chip both include mold compound thereover andtherebetween.
 15. The system of claim 11, wherein said modulated carriersignal is an amplitude-shift keyed (ASK) signal.
 16. The system of claim11, wherein said receiver sense circuitry includes an amplifier: coupledto receive an output of said second tank at inputs of said amplifier;and coupled in series to a rectifier and peak detector and a delayblock.
 17. The system of claim 11, wherein a product of a maximum Qfactor for said first tank and a maximum Q factor for said second tankis ≧50.
 18. The system of claim 11, wherein said modulated carriersignal is at a carrier frequency from 500 MHz to 4 GHz.
 19. The systemof claim 13, wherein said first chip and said second chip are in astacked configuration on a substrate within a multi-chip package (MCP).20. The system of claim 11, wherein said driving said first tank tooscillate comprises applying a periodic wave tuned to said firstresonant frequency modulated by said data.